This invention relates to adaptive filtering and more particularly to multi-channel adaptive filtering.
Multi-channel adaptive filtering appears in several applications like stereophonic or multi-channel acoustic echo cancellation for audio/video conferencing, active noise control, multi-channel equalization, etc. See, for example, xe2x80x9cAcoustic Echo Cancellation Systemxe2x80x9d of Murtaza Ali for which a provisional application Ser. No. 09/261,913 was filed Mar. 3, 1998. This application is incorporated herein by reference. Specially in acoustic echo cancellation and active noise control, the input is not necessarily white (without speech). In such cases, the least mean squares technique has poor convergence rate. On the other hand, the number of filter taps is also very high to allow fast recursive least square (FRLS) like techniques due to high computational complexity (e.g., in multi-channel audio-conferencing, the filter may have thousands of taps). In single channel cases, a class of techniques known as the affine projection algorithm and its fast version have been developed that have low complexity and fast convergence. See Y. Kaneda, M. Tanaka and J. Kojina, xe2x80x9cAn Adaptive Algorithm with Fast Convergence for Multi-Input Sound Control,xe2x80x9d ACTIVE-95, pp. 993-1004, Newport Beach, Calif., July 1995; and S. Gay and S. Tavathia, xe2x80x9cThe Fast Affine Projection Algorithm,xe2x80x9d Proceedings of ICASSP-95, pp. 3023-3026, 1995. Also see Gay U.S. Pat. No. 5,428,562 incorporated herein by reference.
In accordance with one embodiment of the present invention a multi-channel filter system for generating an estimated signal for each channel comprises a forward and backward prediction filter generator responsive to multi-channel input signals for generating a single forward prediction vector signal and a corresponding forward error signal and a single backward prediction vector signal and a corresponding backward error signal. An error generator responsive to errors in the estimated signal multiplies the errors by 1-xcexc for generating error vectors. A pre-filter signal generator responsive to the single forward filter vector signal and corresponding forward error and the single backward filter vector signal and corresponding backward error signal and said error vectors for generating pre-filter coefficients. An adaptive filter output generator coupled to said pre-filter generator and responsive to said pre-filter coefficients and said multi-channel input signals for generating an estimate signal for each channel.